Leadframe-based Ball Grid Array (LFBGA) has the advantages of higher packaging density, lower manufacturing cost, and better thermal dissipation. A leadless leadframe is implemented to replace traditional printed circuit boards or ceramic substrates. Solder balls are disposed on the leads of the leadframe where the solder balls are disposed in an array or in multiple rows to provide electrical connection to an external printed circuit board by SMT. Related technologies have been disclosed by R.O.C. Taiwan Patent No. 529770 and 584316.
An extra reflowing process is required for leadframe-based BGA to solder the solder balls on the leads of the leadframe. However, due to the high reflowing temperatures, the wettibility of the solder balls become better where the solder balls will completely wet the other surface of the leads leading to the insufficient height of the solder balls or even bridging between the leads. A solution is provided by half-etching the leadframes before die-attaching and molding so that only the soldering areas of the leads is protruded then following by encapsulation to encapsulate the other portions of the leads. However, during encapsulation, the only contacting areas of the leads for bonding solder balls are pressed against the molding chest or adhesive tapes, therefore, mold flashes will become an issue. Moreover, since the soldering areas of the leads and the bottom surface of the encapsulant are on the same plane so that mold flash can not easily be detected and removed leading to weakening soldering strength and dropping of solder balls.
Conventional manufacturing processes of leadframe-based BGA packages are disclosed in R.O.C. Taiwan Patent No. 567566. A non-conductive film with through holes to expose the soldering areas of the leads is attached to the bottom surface of the leadframe as solder masks. Since there are gaps between the leads, the non-conductive film must be pre-formed corresponding to the layout of the leads where extra tooling and waste of non-conductive material can not be saved. Furthermore, when attaching the pre-formed non-conductive film to the leadframe, accurate alignment between through holes and the soldering areas is required. Once the through holes of the non-conductive film can not be covered by the leads, encapasulant will flow into the through holes leading to the failure of solder balls placement.